1. Field of the Invention
This invention relates to a semiconductor pressure sensor apparatus and, more particularly, to resin-sealed semiconductor pressure sensor apparatus. This invention also relates to a mold die for use encapsulating the semiconductor pressure sensor apparatus.
2. Description of the Related Art
FIG. 6 is a sectional view showing the process for resin-sealing a known semiconductor pressure sensor apparatus within a mold die. The semiconductor pressure sensor apparatus as shown includes: a semiconductor pressure sensing element 1; a stem (seating base) 8 which is formed, for example, of iron or kovar and to which the semiconductor pressure sensing element 1 is firmly fixed by means of die-bonding or the like; signal lines 10 extending through the stem 8 for outputting to the outside an electrical signal indicating a pressure detected by the semiconductor pressure sensing element 1; and bonding wires 3 for electrically connecting each signal line 10 to the semiconductor pressure sensing element 1. As shown, the apparatus is encapsulated, i.e., resin-sealed, by a resin 2, such as an epoxy resin, within a resin-sealing mold die 4, 9. Here, a part of the surface of the semiconductor pressure sensing element 1 is not resin-sealed in order to be serve as a pressure detecting portion. The resin-sealing mold die 4, 9 is constituted by two mold halves, i.e., an upper mold 4 and a lower mold 9. The upper and lower molds 4 and 9 together form a cavity (space) 11 for holding the semiconductor pressure sensing element 1 to seal it in the resin. Further, an injecting groove 5 for injecting a resin is formed on a lower portion of the upper mold 4, as shown in FIG. 6 by a dotted line.
A method for sealing the apparatus will now be described in further detail. The semiconductor pressure sensor apparatus after both the die bonding process with the above described stem 8 and the wire bonding process with the wire 3 is inserted into the cavity 11 as shown in FIG. 6 which is formed by the upper and lower molds 4 and 9 as mentioned above. In this state, as the resin 2 is injected into the cavity 11 through the injecting groove 5, the apparatus is resin-sealed under pressure.
In the known semiconductor pressure sensor apparatus manufactured as described above, a gap 12 between the stem 8 and the mold die 4, 9 sometimes occurs due to variations in the thickness of the stem 8 or deformation and wear due to abrasion in the surface of the mold die 4, 9. In such a case, the resin 2 undesirably enters the gap 12 in the molding process so as to form a flash or burr 13 (see FIG. 7) of the resin, resulting in a problem that the undesirable flash 13 remains as unwanted resin on the surface of the stem 8.
Since the molded semiconductor pressure sensor apparatus is welded to a metal package 20 at an outer peripheral portion 8aa of the stem 8, as shown in FIG. 7, when the resin flash 13 is present on the outer periphery 8aa of the stem 8, a partial gap occurs between the outer periphery 8aa and the metal package 20. A pressure transmitting fluid medium 22, such as silicone oil filling in a pressure transmitting path 21 within the metal package 20 leaks to the outside from such gap, resulting in a problem that the reliability of apparatus is lowered by the undesirable resin flash 13.
For this reason, in the known semiconductor pressure sensor apparatus, the flash 13 has been removed by mechanical polishing. However, the resin flash 13 adhered to the stem 8, which is made of a metal such as iron is highly adhesive and it is difficult to remove it. Further, its manufacturing process becomes complicated because removal of the resin flash 13 is required. Accordingly, its manufacturing cost is increased, and results in a higher price for the product.